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364                             Poissoris Ratio.

TABLE OF ELASTIC MODULI (units being inches and Ibs.).

Material.
	E.
	C.
	K.

Cast Steel Forged Steel ...
	30,000,000 30,000,000
	12,000,000 I3,OOO,OOO
	> 26,000,000

Steel Plates    ...
	31,000,000
	13,000,000
	...

Mang. Bronze.,.
	
	.*.
	

W.I. Bars W.I. Plates    ...
	29,000,000 26,000,000
	IO,5OO,OOO 14,000,000
	[ 20,000,000

Copper   ......
	12,000,000
	
	24,000,000

Gun Metal     ...
	13,500,000
	
	

Cast Iron
	I7,OOO,OOO
	6,300,000
	14,000,000-

Brass      ......
	13,500,000
	
	15,000,000

Muntz Metal ...
	I4,OOO,OOO
	5,250,000
	

Water     ......
	,           -
	...
	300,000

Mechanical treatment may raise these ratios: for tempered steel
E = 36,000,000 and C = 14,000,000, while for rolled or drawn
copper E = 15 or 17 millions respectively. (See App> V^ p. 996.)
Poisson's Ratio (M) is a constant to determine the lateral
effect of direct stress. If a bar, as in Fig. 323, be extended or
compressed, it undergoes lateral contraction at A and expansion
at B. Then, within the elastic limit:

Direct strain == lateral strain x M
t or Sc = 61 x M

TABLE OF POISSON'S RATIO.

Material.

M.

Steel   ...        ...       ......
	

Wrought Iron ...
	r6

Cast Iron       ,..        .        ...        .,, Copper
	a v
 3*7

Brass  ...
	3*0


	

Nature of Shear Stress.If tfee bar in Fig. 324 be sub-
jected to elastic shear stresses, j s an equal pair of shear stresses